Inaccurate Blood Flow Rate During Rapid Hemodialysis

Simulated hemodialysis with isotonic saline was performed to compare the requested blood flow rate (BFR-r) with the actual blood flow rate (BFR-a) delivered during rapid, efficient hemodialysis. Four different blood pumps and blood lines from three different manufacturers were used for the studies. BFR-r was set on each blood pump, and a timed outflow specimen from the dialysis circuit was used to measure the BFR-a delivered. BFR-r values of 200, 350, and 500 mLlmin were used; the arterial pressure was set at − 50, − 250, and − 325 mm Hg. BFR was determined every hour for 5 hours. At an arterial pressure of −50 mm Hg, the BFR-a was slightly higher than the BFR-r, and this did not vary over the 5-hour study period. When the arterial pressure was − 250 mm Hg, the initial BFR-a was 95% of the BFR-r; at the end of the 5-hour study, this had declined to an average of 87% of the BFR-r. The largest discrepancy between BFR-a and BFR-r was at an arterial pressure of − 325 mm Hg; the initial actual values averaged only 90% of the requested, and by the end of the 5-hour study, this value had declined to a mean of 78% of the BFR-r. The use of whole blood with a hematocrit value of 33% and the addition of venous reistance did not significantly affect these results. Our studies demonstrate that the BFR-a can be much lower than the BFR-r during rapid, efficient hemodialysis, which uses high BFRs and arterial line negative pressures. This phenomenon may be a cause of inadvertent underdialysis during this procedure.